Vehicle bus control system

ABSTRACT

A vehicle power bus control system including a control module having a communication interface and a device having a communication interface for communicating with the control module wherein the control module is adapted to transfer at least one electrical limit value to the device, and wherein the device is adapted to act in response to the electrical limit value to self-regulate an electrical quantity associated with the device.

TECHNICAL FIELD

The present invention relates to bus control systems used in vehicles.

BACKGROUND

Modern vehicles are much more complex than vehicles produced as recentlyas twenty years ago. One of the most complicated aspects of modernvehicles includes electrical power management amongst systems andcommunications between systems. In fact, communication between andamongst a vehicle's various systems and subsystems is often implementedusing high speed serial bus communication techniques. One such popularserial bus protocol implemented on many vehicle systems is known as theCAN (Controller Area Network) protocol. The CAN protocol is amulti-master protocol for efficiently communicating serial data betweena vehicle's systems and subsystems. Other vehicle bus communicationprotocols are also known such as LIN, MOST, and FLEXRAY. The complexityof vehicle electrical control systems has been exacerbated in recenttimes by the proliferation of hybrid vehicles. Hybrid vehicles dependupon the combination of both a fossil fuel powered engine and anelectric motor to generate a vehicle's propulsion forces.

The efficiency gains promised by hybrid vehicles may in part be attainedby the proper monitor and control of the electrical power consumed orgenerated by one or more vehicle subsystems. It may also be desirable toassign priorities to the various subsystems so that when power demandedby a hybrid vehicle's systems exceeds the vehicle's power generationcapability, the highest priority systems can be kept in service whilethe electrical load imposed by the lower priority systems can belightened or eliminated.

SUMMARY

A vehicle power bus control system including a control module having acommunication interface and a device having a communication interfacefor communicating with the control module wherein the control module isadapted to transfer at least one electrical limit value to the deviceand wherein the device is adapted to act on the electrical limit valueto self-regulate an electrical quantity associated with the device.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic view of a vehicle bus control system according toan embodiment of the present invention.

FIG. 2 is a schematic view of a device used in conjunction with thesystem of FIG. 1 according to an embodiment of the present invention.

FIG. 3A is a table showing exemplary communication information that maybe broadcast by the control module to one or more devices, according toan embodiment of the present invention.

FIG. 3B is a table showing exemplary information that may be broadcastfrom one or more devices to the control module according to anembodiment of the present invention.

FIG. 3C is exemplary information that may be broadcast from the controlmodule to specific devices, according to an embodiment of the presentinvention.

FIGS. 4A and 4B are logic flow diagrams depicting exemplary steps thatcan be carried out in a start up and run procedure in an embodiment ofthe present invention.

FIG. 5 is an exemplary procedure for allocating electrical power/currentamongst devices according to an embodiment of the present invention.

FIG. 6 sets forth exemplary steps that may be implemented in a shut downprocedure according to an embodiment of the present invention.

DETAILED DESCRIPTION

Now referring to FIG. 1, vehicle bus control system 10 includes one ormore batteries 12 which can be used to provide electrical power to oneor more electrical devices 14, 16, 18, and 20. Electrical devices 14,16, 18, 20 are electrical joined to battery 12 by way of one or morebusses 22, 24. For example, certain classes of devices (electricalaccessories 16, 18, 20) can be connected to battery 12 by way ofaccessory power sub-bus 22 (only one sub-bus is shown in FIG. 1) whereasother classes of devices (such as motor controller 14), can be connectedto battery 12 by way of power bus 24. Although only one sub-bus 22 isshown in FIG. 1, the present invention contemplates the use of one ormore sub-busses. For the purpose of this disclosure, a device is anyelectrical component or system that includes a bus interface while anelectrical accessory is any electrical component or system that, atleast in a mode of its operation, draws electrical energy from, orsources electrical energy to, accessory power sub-bus 22.

Electrical accessories 16, 18, 20 are connected to battery 12 by way ofjunction box 26. Junction box 26 may contain one or more fuses 27 whichare appropriately sized to protect the electrical conductors servicingthe accessories 16, 18, 20 along the accessory power sub-bus 22.Junction box 26 may also contain an isolator device 28 that is used toelectrically isolate accessory power sub-bus 22 from battery 12 in theevent that one or more electrical accessories 16, 18, 20 malfunctions ina manner that warrants disconnecting all accessories 16, 18, 20 frombattery 12. In its simplest embodiment, isolator device 28 includes arelay coil coupled to relay contacts 28′. Isolator device 28 may bewired in series (i.e. “daisy chained”) to each drop out relay contact16′, 18′, 20′ by way of hardware fault line 21. The ends of the chainmay be connected to drivers 23, 27 which may be controlled by controlmodule 32 by supplying current (through fault line 21) or by monitoringthe state of hardware fault line 21 (by monitoring the voltage at sensorpoint 25). If one or more of the accessories 16, 18, 20 detect acondition which justifies electrically removing accessory power sub-bus22 from battery 12, the affected accessory 16, 18, 20 can open itsrespectively associated drop out relay contact 16′, 18′, 20′ whichdisengages isolator device 28 which, in turn, causes contacts 28′ toopen thereby electrically disconnecting accessory power sub-bus 22 frombattery 12. Hardware fault line 21 is not under the sole control ofcontrol module 32. Accordingly, if control module 32 fails, accessories16, 18, 20 can still activate isolator device 28.

Each drop out relay contact 16′, 18′, 20′ is daisy chained together byway of hardware fault line 21 and the end of the daisy chain is loopedback and terminates at a low side driver 23. Low side driver 23 can becontrolled by control module 32. If any accessory 16, 18, 20 detects afault that requires immediate disconnection of the accessory fromaccessory power sub-bus 22, the effected accessory 16, 18, 20 will,amongst other things, open its respective drop out relay contact whichin turn will cause the isolator device 28 to disconnect the accessorypower sub-bus 22 from the battery 12.

During start up mode before accessory power sub-bus is energized,control module 32 may perform system tests including a hardware faultline test. The hardware fault line test can be conducted by using thecontrol module to send sequential communications along communication bus30 to each accessory 16, 18, 20 sequentially asking each accessory 16,18, 20 to activate its drop out relay contact 16′, 18′, 20′.

In addition, it might be advantageous if one or more accessories has thecapability to monitor the voltage on the downstream side of itsrespective drop out relay contact 16′, 18′, 20′. This may beparticularly important for accessory devices that have the ability tosource current into the accessory power sub-bus. If it is desirable foran accessory to have the capability to monitor the voltage on thedownstream side of its drop out relay contact, a sense line 16″″, 18″″,20″″ can be monitored by each respective accessory 16, 18, 20. If anaccessory 16, 18, 20 detects that the downstream side of itsrespectively associated drop out relay contact 16′, 18′, 20′ is notconnected to ground, the device can be programmed to discontinuesupplying power to the accessory power sub-bus 22 or it can beprogrammed to initiate any number of additional procedures that might bebeneficial.

Most devices 14, 16, 18, 20 have at least one mode of operation in whichthey consume electrical energy (i.e. they require electrical current tobe provided to them from their respective bus 22, 24 in order to performsome, or all, of their functions). However, some devices may be capableof sourcing electrical current into their respectively associated bus22, 24 in some modes of operation. For example, when it is desirable toreduce the speed of the vehicle, motor controller 14 can utilize primemover (hybrid vehicle electric motor) 15 in a way that causes primemover 15 to generate electrical current. This electrical current can becoupled to battery 12 by power bus 24 and, in turn, be used to increasethe state of charge of the battery 12. Also, it is contemplated that atleast one accessory 16, 18, 20 might be an alternator for maintainingbattery 12 in a sufficient state of electrical charge.

It may be desirable to stipulate a maximum electrical property (e.g.capacitance, resistance, and inductance) of each electrical device 14,16, 18, 20. This might be desirable so that system 10 is capable ofsourcing, at startup, the initial current draw of each device 14, 16,18, 20 without causing an unacceptably high current transient flow or anunacceptably large inductive kickback (at shutdown). Also, stipulating amaximum capacitance, resistance, and inductance might also beadvantageous if the sub-bus must be disconnected quickly in anemergency. Once the busses 22, 24 have been connected to the batteryand, the initial current transients have subsided, the electricalproperties of each electrical accessory 16, 18, 20 may, if it'sdesirable, be switched to more advantageous operating values. In thecase where one or more electrical accessories 16, 18, 20 have a largeinternal capacitance, these devices may require an internal pre-chargecircuit that can be activated after their respective bus 22, 24 has beenenergized. Also, it may be desirable for each accessory 16, 18, 20 toprovide sufficient electrical isolation (i.e. ohmic resistance) betweeneach accessory 16, 18, 20 and other vehicle components (such as vehiclechassis, positive and negative supply rails, etc.).

Each device 14, 16, 18, 20 can be provided with a bus interface 14″,16″, 18″, 20″. Other devices, such as junction box 26 and battery 12 canalso be coupled to their own respectively associated bus interfaces 12″,26″. Each bus interface 12″, 14″, 16″, 18″, 20″, and 26″ communicatesalong a common communication bus 30. Communication bus 30 also connectsto control module 32. Control module 32 also includes its ownrespectively associated bus interface 32″. All devices 12, 14, 16, 18,20, and 26 that are connected to communication bus 30 may communicatewith control module 32 by way of a common bus communication protocol(such as the CAN protocol). If any device 12, 14, 16, 18, 20 or 26 failsto comply with the predetermined communication protocol, action can betaken by the device itself (by way of self diagnostics) or by thecontrol module 32 to disconnect the non-compliant device from itsassociated bus 22, 24. The disconnecting action may be accomplished byusing the control module 32 to send the appropriate command to theoffending accessory over communication bus 30. Although specific mentionhas been made herein to the CAN bus protocol, the present inventioncontemplates the use of any appropriate communication protocol.

Now referring to FIGS. 1 and 2, each accessory 16, 18, 20 may include arespectively associated bus interface 16″, 18″, and 20″. Additionally,other devices (such as battery 12, motor controller 14, and junction box26) may also include respectively associated bus interfaces 12″, 14″,and 26″ for reporting various operational values to control module (suchas power from/to battery, power from/to hybrid motor, etc.). Eachelectrical accessory 16, 18, 20 includes a respectively associated businterface 16″, 18″, 20″. Each bus interface 16″, 18″, 20″ interfaceswith a respectively associated operating unit. For example, accessory 16might contain a radio receiver operating unit, electrical accessory 18might contain an air conditioning unit operating unit, and electricalaccessory 20 might contain an ABS operating unit. Each operating unit16′″ 18′″, and 20′″ is capable of placing information on communicationbus 30 by way of it's respectively associated bus interface 16″, 18″,20″. Information placed on communication bus 30 by one or more accessory16, 18, 20 is primarily intended to be received by control module 32;however, it is contemplated within the scope of this invention thataccessories 16, 18, 20 can place information on communication bus 30which is intended for receipt by other devices 12, 14, 16, 18, 20, 26joined to communication bus 30 by way of a respectively associated businterface.

By way of example, and without limitation, each accessory 16, 18, 20 maybe capable of placing information on communication bus 30 which isparticular to that accessory's state. For example, each accessory 16,18, 20 may from time to time report to control module 32 the actualelectrical energy 33 being consumed by the accessory as provided bypower sub-bus 22. The format for reporting the energy consumption of anaccessory can be formatted in any number of ways including for example,power averaged over a given interval, average maximum power consumedand/or average minimum power consumed, or any other meaningful measureof power or proxy therefore. There may be occasions where it isadvantageous to report to control module 32 the electrical current thatan accessory 16, 18, 20 is drawing from bus 22 or to report the voltagedrop across an accessory 16, 18, 20. Additionally, each accessory 16,18, 20 may be adapted to report its priority setting or request areallocation of its priority setting 34. Of course control module 32 maynot be obligated to honor a priority request reassignment but may do soif appropriate. It is envisioned that in most applications, the finalarbiter of an accessory's priority allocation will be a centralcontroller (such as control module 32).

Each accessory 16, 18, 20 is capable of receiving an upper electricallimit command setting 36 from control module 32. This upper electricallimit command setting 36 is used by operating unit 16′″, 18′″, 20′″ toset the uppermost electrical consumption allowed by accessory 16, 18,20. Electrical consumption can be quantified in units of energy, power,current, voltage or any other electrical quantity that may beappropriate. If, during the normal operation of accessory 16, 18, 20,control module 32 detects that a particular accessory 16, 18, 20 hasexceeded its upper electrical limit command setting 36, control module32 can be programmed to take any number of actions including disablingthe function of the accessory 16, 18, 20 and/or disabling its electricalconnection to bus 22.

Not only is each accessory 16, 18, 20 capable of requesting areallocation of its priority setting 34, but it is also capable ofreceiving a priority command 38 from control module 32. The controlmodule 32 carries out a priority allotment procedure for determining themaximum electrical consumption or maximum electrical generationallocated to each accessory. If insufficient electrical supply exists tofill the total demand of all devices, then control module 32 may commandone or more lower priority devices to isolate themselves from bus 22. Inthe alternative, control module 32, may be used to issue a reduced powercommand consumption allocation to one or more devices (by reducing adevice's upper electrical limit command setting). The system 10 can bedesigned such that the devices 12, 14, 16, 18, 20, and 26 can requestthat the system generate power specifically for their consumption;however, these requests do not have to be followed by the controlmodule. Devices that are capable of sourcing electrical energy into oneor more bus 22, 24 must not exceed their lower (or negative) electricallimit command setting 36 and, like power consuming devices, they can berequired to report the quantity of electricity they are returning totheir respective bus 22, 24.

Although it is not required in carrying out the present invention, theremay be distinct advantages in assigning each device its own uniquesource address (with respect to bus 30). Furthermore, there may beadvantages in designing system 10 such that accessories and devices are“arbitrary address capable” since preferred addresses for manyaccessories and devices may not be established or defined at the timethe system is designed. By enabling the accessories 16, 18, 20, to be“arbitrary address capable”, the control module 32 can respond to anydevice irrespective of the device's source address as long as the devicecomplies with the bus communication protocol. This will enable system 10to accept add on devices even after the system is operating in thefield.

Although some of the communications between accessories 16, 18, 20, andcontrol module 32 are discussed in conjunction with FIG. 2, FIGS. 3A-3Cset forth examples of the type of information exchange that can takeplace between the control module and the accessories and devices. Someof the status broadcasts may have multiple fields. For example, the “BusStatus” broadcast shown in FIG. 3A has three distinct fields (each fielddelimiter is shown as a semicolon in FIG. 3A). The information set forthin FIGS. 3A-3C is meant to be exemplary and not exhaustive.Additionally, it is contemplated that some of the accessories and someof the devices may not be required to communicate some, or any, of theinformation discussed in conjunction with FIGS. 2, 3A, 3B, and 3c.

Control module 32 and devices 16, 18, 20, 26, 12, and 14 may beconfigured to contain internal processing units that control theirfunction. Generally, these internal processing units have a power downstate, during which their internal control logic is not operating. Inorder to “awaken” the internal processing unit, some initiating signalis provided to the device that causes it to commence power up andthereby initiate an internal logic sequence. The source of theinitiating signal may be one or more sources of, for example, a userinput (such as a certain position on the ignition key switch), a signalfrom some other device, the control module 32, or an internal timer.Throughout this disclosure, the initiating event(s) will be referred toas the “power up conditions.”

The startup and run procedure will now be discussed in conjunction withFIGS. 4A and 4B respectively. Upon detecting assertion of one or morepower up conditions, each control module 32 begins its power-up sequenceand the control module 32 may send one or more general broadcastmessages 42 to all bus interface enabled devices 12, 14, 16, 18, 20, 26.Some of the types of general broadcast messages that the control module32 may send are found in FIG. 3A. The general status broadcast examplesgiven in FIG. 3A are exemplary and they are not required in implementingthe present invention. Also, it is contemplated that general broadcaststatus messages in addition to the ones shown in FIG. 3A can also beimplemented.

Upon power up, all devices having a bus interface may perform one ormore internal self tests 44 and announce their presence to the controlmodule 32. At some point during the startup procedure, control module 32may assign a priority to one or more devices and may send each device 46its assigned priority. There may be no need for the control module 32 toassign a priority to devices that are not power consumption devices. Forexample, it is contemplated that some of the devices (e.g. junction box26) will not be a power consumption devices and accordingly it may notserve a purpose to assign a priority to a non-power consuming/producingdevice.

During startup, the control module 32 may be programmed to conduct testson each accessory 16, 18, 20. One such test, for example, may be carriedout by using control module 32 to send 48 the appropriate command alongcommunication bus 30 thereby requesting each accessory to activate itsrespectively associated dropout relay contact 16′, 18′, 20′. Byconducting such a test 48, control module 32 can ensure that theisolator device 28 will effectively isolate accessory bus 22 frombattery 12 if a hardware fault develops in any of the accessories 16,18, 20.

If the dropout relay test of step 48 is successful, control module 32may initiate pre-charging 50 of the accessory bus 22. Junction box 26,may include hardware to pre-charge the accessory power bus 22 beforeengaging the main contactors 28′. One way to pre-charge accessory bus 22is to use junction box to “source” a limited current into the accessorybus, possibly through one or more resistive bridges connected to battery12, in order to slowly bring the bus voltage up to a minimum value.Alternatively, devices 12, 14, 16 may be configured so that nopre-charge circuit is necessary in the junction box. The pre-chargingprocess can be monitored 52 by circuitry located in the junction box, orcontrol module 32 to detect when the minimum voltage threshold has beenreached (effectively indicating that it is appropriate to connect themain contactor). Once the main contactor 28′ is connected 54, theaccessory power bus is fully energized to the potential established bybattery 12.

Once the accessory power bus 22 has been fully energized, theinitialization sequence is finished, and the control module 32 maypermit 58 one or more of the accessories 16, 18, 20 to draw electricalenergy within the limits defined by the maximum positive and maximumnegative electrical limit command 55 as established by the controlmodule 32. It is also contemplated, in devices where it is appropriate,that power to a device can be applied (or withdrawn) gradually (i.e.ramped over time) to prevent current surging at startup or currentspikes at shutdown.

While managing the loads as described in the run procedure FIG. 4B, thecontrol module 32 may sum all of the power/current actually consumed bythe accessories (control module 32 can be interfaced to the accessorypower sub-bus, or to each power producing device such that it canmonitor how much power/current passes through bus 22, 24) and comparesthat value to the power/current consumption of the devices as theyreport it to the control module 32. If the power/current actuallyconsumed/produced does not agree (within a defined limit) to thepower/current as monitored, a status flag can be set reflecting that thepowers/currents do not sum and the appropriate fault routines can beexecuted. Any number of actions can be undertaken in such a faultroutine including, for example, warning the vehicle operator orpreventing the vehicle from running. Additionally, control module 32could examine the reported power/current consumption of each device toensure that each device is operating within the prescribed limits oftheir power/current consumption restraint set by control module 32. Ifone or more devices exceeds the prescribed limits of theirconsumption/generation allotment (as defined by the limit command),appropriate steps can be taken such as warning the vehicle operatorand/or disabling the device.

It is important to note that during a normal mode of power management,the control module 32 may issue 56 to each device a maximum positiveelectrical limit command and, where appropriate, a minimum negativelimit command. Once each device is provided with the positive andnegative electrical limit command, it is the responsibility of eachdevice, not the control module 32, to manage its own (i.e.self-regulate) electrical consumption/generation of power or currentwithin the limits defined by the maximum positive and maximum negativeelectrical limit command. In cases where a particular device cannotmaintain full functionality while honoring the constraints of itselectrical limit command defined by control module 32, it may request,from control module 32, an expansion of its positive or negative limitcommand values. Of course, depending on the prevailing conditions andthe algorithm used by control module 32, control module 32 may determinethat it is not prudent or otherwise desirable to honor the request ofthe device. In some applications, it may be desirable under well definedcircumstances to allow certain devices to exceed the positive ornegative limit commands issued by the control module 32; however, in thevast majority of applications, it is contemplated that in order for asingle, centralized controller to effectively coordinate properpower/current flow within system 10, it will be desirable for controlmodule 32 to be the final arbiter of electrical consuming/sourcingdecisions.

In order for the control module to carry out one or more of itscentralized monitoring tasks, one or more devices may, from time totime, report their actual power consumption to control module 32 by wayof bus 30. In view of this reporting/accounting feature, control module32 can determine if there are one or more devices attached to accessorypower sub-bus 22 or bus 24 which are not properly registered. Forexample, if a device is attached to accessory power bus 22 but it is notparticipating in the bus protocol (e.g. does not communicate withcontrol module 32 along bus 30), the device will still drawpower/current from the accessory power sub-bus 22. Control module 32 mayhave the capability of measuring total system current i₃ by virtue of,for example, bus interface 12″ connected to battery 12. However, whencontrol module 32 computes the sum of the accessory currents (i.e.i₁+i₂+ . . . i_(n)), as they are reported to control module 32 by eachaccessory 16, 18, 20, the reported currents will not equate to themeasured current i₃. Accordingly, control module 32 will be capable ofdetecting that there are unauthorized devices attached to the accessorypower sub-bus or perhaps one or more devices have malfunctioned. Ineither case, any number of actions can be initiated including, forexample, notifying the vehicle driver or disabling the vehicle ignition.

Any number of priority algorithms can be used for allocating electricalenergy amongst the devices 12, 14, 16, 18, 20. An example of one suchpriority algorithm is set forth in FIG. 5; however, other priorityalgorithms may also be suitable depending on the control strategy to beimplemented in system 10. In some applications, it might be helpful ifthe priority algorithm considers whether the vehicle is moving 62. Forexample, if a vehicle is not moving, it may be acceptable to allocateless electrical energy to a particular device than it would otherwise beif the vehicle is moving. For example, if the vehicle is not moving, itmay be acceptable to allocate very little electrical energy to thevehicle brake system. Obviously, if the vehicle is moving, it may neverbe appropriate to allocate less than full electrical energy to thevehicle brake system. If it is determined that the vehicle is stopped,control passes to logic step 64 where the control module 32 receiveseach accessory's required power/current request. If the sum of eachaccessory's required power/current request is greater than thepower/current that the system can supply, the logic of step 68 isexecuted wherein the power/current requests of the highest prioritydevices are granted and the power/current requests of the lowestpriority devices are denied 68 their request. In some applications,depending on the device, it may be acceptable for a device to operate atpartial power/current. For example, if all of the power/currentrequested by a low priority device cannot be granted by control module32, it may be possible for control module 32 to grant permission for adevice to draw a portion of the power/current requested by a lowpriority device. In the case, for example, where the low priority deviceis a radio, it may be perfectly satisfactory to operate the radio at areduced power/current (in some cases this may only adversely affect themaximum volume obtainable from the radio and may not adversely affectthe operation of the radio). However, some devices are “all or nothing”type devices and may not operate satisfactorily with reducedpower/current and they may not be manipulatable in this way. In the caseof “all or nothing” devices, operating at less than full power may notbe an option. If the total power/current required by the devices is notgreater than that which can be supplied, step 70 is executed and controlmodule 32 may authorize all devices to consume the power/current theyhave requested up to and including the maximum power/current allottedfor the device.

Steps 72, 74, 76 are parallel to steps 64, 68, and 70 respectivelyexcept that a different priority scheme can be used in 74 to order thehighest priority devices. For example, when the vehicle is not stopped,logic step 74 may set the highest priority to accessories such assteering, braking or other critical chassis functions and may setintermediate priorities to power generation (120 volts AC hotel loads)and climate control (A/C compressor) systems. Other lower priorities maybe assigned to the radio and the like. For logic step 68 wherepriorities must be assigned to a vehicle that is stopped, there may notbe a need to assign steering and braking with the highest priority.

The accessories 16, 18, 20 may be designed such that they can, whenappropriate, request a priority reallocation from control module 32. Forexample, it may be appropriate in certain system designs for anaccessory to have a low priority under certain circumstances but underother circumstances the same accessory could be justified in requiring ahigh priority. Such an algorithm could be included in the priorityalgorithm of FIG. 5 so that system 10 can be adaptable in any number ofcircumstances.

Now referring to FIG. 6, shutdown begins 78 when control module 32commands each accessory to ramp its power consumption/generation down toa predetermined level. This ramping down can be programmed to take placegradually over a predetermined period of time. In many cases, thispredetermined level will be zero power consumption/generation. However,non-zero power levels might be appropriate in certain circumstances.Once the power consumption of each accessory device has reached itspredetermined level 82, the control module 32 can de-energize theaccessory bus 83 and thereafter the control module 32 can itself bepowered down 84. Once rampdown is complete 82, each accessory, whereappropriate, can be placed in a state suitable for precharging 88(thereby preparing it for the next start up). Lastly, each accessory 16,18, 20 opens its respective drop-out relay contact 16′, 18′, 20′ therebyopening 91 hardware fault line 21. Although examples of normal modes ofoperation have been discussed in conjunction with FIGS. 4, 5 and 6,there are times where when exceptional conditions may prevail. Underexceptional conditions, extreme measures may be prudent. For example, incases where control module 32 ceases from receiving bus communicationsfrom a device, the appropriate fault can be raised by control module 32(such as a “currents do not sum” fault). Under some conditions, it maybe appropriate to wait a predetermined period of time to determine ifthe fault condition “corrects itself.” In cases where a device losesmessage communication with the control module, it might be appropriatefor the device to go into a shut down mode where the accessorydisconnects itself from the accessory bus 22. In cases where the“currents do not sum” fault is active, it might be appropriate to simplywarn the driver of the presence of the fault condition especially if thevehicle is in motion or the transmission is in gear. Under theseconditions, it might be prudent to continue to supply power to thesub-bus 22. If the “currents do not sum” fault is active and the vehicleis stopped, and the transmission is in neutral or park, it might beappropriate to program the control module 32 to disconnect the accessorybus 22 from battery 12.

The present invention has been particularly shown and described withreference to the forgoing embodiments, which are merely illustrative ofthe present invention and are not meant to be restrictive. For example,some functional distinctions have been made herein between devices suchas accessories, 16, 18 and 20 and devices such as battery 12, motorcontroller 14, and junction box 26. All of these devices can include abus interface which allows them to communicate with control module 32.However, in some cases (depending on the particulars of the electronichardware used within the device or the device's operating unit), some orall of the functionality that has been described in conjunction withaccessories 16, 18 and 20 may not be appropriate for other types ofdevices (such as battery 12, junction box 26, motor controller 14).Also, much explanation has been presented regarding the power/currentrequested by a device and the power/current consumption permitted by thecontrol module 32. The use of the term “power” throughout thisapplication should not be construed solely accordingly to the technicaldefinition of electrical power (i.e. wattage). It is known to thoseskilled in the art that other metrics for measuring electrical energytransfer (e.g. current, voltage, magnetic field strength, etc.) canoften be used as surrogates or proxies for traditional energymeasurement techniques (especially when they are combined with certainassumptions) and still offer sufficient estimation of electrical energyflow to carry out the spirit of this invention. Additionally,communication bus 30 has been shown and discussed in the context of atangible bus (i.e. a bus fabricated from copper conductors, opticalfibers, and the like). However, nothing in this disclosure should beinterpreted to limit bus 30 to a tangible bus structure and it iscontemplated that bus 30 can also include any wireless communicationsystem that is effective for facilitating information transfer betweenand amongst devices or between devices and control module 32.

It is intended that the following claims define the scope of theinvention and that the method and apparatus within the scope of theseclaims and their equivalent be covered thereby. The description of theinvention should be understood to include all novel and non-obviouscombinations of elements described herein and claims may be presented inthis or later applications to any novel and non-obvious combination ofthese elements. Moreover, the foregoing embodiments are illustrative andno single feature or element is essential to all possible combinationsthat may be claimed in this or a later application.

1. A vehicle power bus control system, comprising: a control modulehaving a communication interface, a device having a communicationinterface for communicating with said control module, wherein saidcontrol module is adapted to transfer at least one electrical limitvalue to said device, and wherein said device is adapted to act inresponse to said at least one electrical limit value to self-regulate anelectrical quantity associated with said device.
 2. The vehicle buscontrol system of claim 1, wherein said communication interface of saidcontrol module and said communication interface of said devicecommunicate with each other by way of a serial bus.
 3. The vehicle buscontrol system of claim 1, wherein said device includes first and seconddevices adapted to communicate between each other and to communicatewith said control module.
 4. The vehicle bus control system of claim 3,wherein said control module is adapted to determine if one of the firstand second devices is participating in a communication protocol.
 5. Thevehicle bus control system of claim 1, wherein said device has anassociated priority and wherein said device is adapted to send a requestto said control module requesting a reassignment of its associatedpriority.
 6. The vehicle bus control system of claim 1, wherein saiddevice includes a hardware fault line that is not under the sole controlof said control module.
 7. The vehicle bus control system of claim 1,wherein the device is adapted to modify at least one of its internalelectrical states including an internal capacitive, resistive orinductive state.
 8. A method of controlling a plurality of devicescoupled to an electrical power bus, comprising the steps of: i) using atleast one of the plurality of devices to report a request to a controlmodule, ii) determining, within said control module, whether to honor atleast some of the requests reported by the devices in step i), iii)disseminating to one or more of the devices of step i), at least onelimit value, iv) using at least some of the devices in step i) to limitat least one of their own respective electrical constraints relative tothe electrical power bus.
 9. The method of claim 8, wherein the requestsreported to the control module by at least one of the devices, containinformation relating to at least one of an electrical current, voltage,or electrical power that each at least device desires to be providedwith from the electrical power bus.
 10. The method of claim 8, whereinthe determining step further includes assigning a priority to at leastsome of the plurality of devices.
 11. The method of claim 8, wherein thedetermining step further includes determining if one or more deviceshave requested a reassigned priority.
 12. The method of claim 8, whereinsaid disseminating step includes disseminating at least one of apositive maximum current value, or a positive maximum power value. 13.The method of claim 8, wherein said disseminating step includesdisseminating at least one of a negative maximum current value or anegative maximum power value.
 14. The method of claim 8, wherein thedetermining step further includes determining an actual current or anactual power associated with at least some of the devices.
 15. Themethod of claim 8, further including detecting a fault condition anddisseminating a command to at least one device, wherein the commandincludes commanding the at least one device to electrically isolateitself from said electrical power bus.
 16. The method of claim 8,further including the step of providing to said control module, ameasurement of an actual electrical quantity transferred between atleast one of said devices and said electrical power bus.
 17. The methodof claim 8, wherein said determining step includes determining whether atotal electrical quantity required by at least one of the pluralitydevices is greater than a total power that can be supplied by theelectrical power bus.
 18. The method of claim 17, further includingdetermining whether a vehicle associated with the electrical power busis stopped.
 19. The method of claim 8, wherein the determining stepfurther includes assigning different priority values to two or moredevices wherein the different priority values are based on a criticalityof a function carried out by an operating unit respectively associatedwith each device.
 20. The method of claim 8, wherein the disseminatingstep further includes using the control module to disseminate to one ormore devices, one or more self-test commands.